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United States Patent |
5,132,624
|
Kitson
|
July 21, 1992
|
Method and apparatus for insulating electrical devices in a logging
sonde using a fluorinated organic compound
Abstract
A method for providing electrical insulation to electrical devices (e.g.
connectors) disposed at the end of the housing of a logging sonde designed
to be lowered in a borehole traversing earth formation, wherein the
housing is at least partly filled in with an insulating fluid having a
density greater than the borehole fluid density. Advantageously, the
insulating fluid density is greater than the density of water. Preferably,
the housing is filled with a mix of insulating oil and hydraulic oil
having a density less than the insulating oil density. The amount of
insulating fluid is such that it covers the electrical devices when the
sonde is substantially in the upright position. The insulating fluid is
e.g. made of a fluorinated organic compound, such as the oil sold under
the name Fluorinert.RTM. (trademark of 3M).
Inventors:
|
Kitson; David (Plano, TX)
|
Assignee:
|
Schlumberger Technology Corporation (Houston, TX)
|
Appl. No.:
|
626341 |
Filed:
|
December 12, 1990 |
Current U.S. Class: |
324/339 |
Intern'l Class: |
G01V 003/28 |
Field of Search: |
324/338-343
|
References Cited
U.S. Patent Documents
3719918 | Mar., 1973 | Kerr.
| |
4598967 | Jul., 1986 | White.
| |
4651101 | Mar., 1987 | Barber et al.
| |
4701712 | Oct., 1987 | Seeley et al. | 324/340.
|
4767349 | Aug., 1988 | Pottier et al.
| |
4817437 | Apr., 1989 | Dennis et al.
| |
4872507 | Oct., 1989 | Ronco, Sr. et al.
| |
Primary Examiner: Snow; Walter E.
Attorney, Agent or Firm: Garrana; Henry N., Bouchard; John H.
Claims
What is claimed is:
1. A method for providing electrical insulation to electrical devices
disposed at one end of a housing of a logging sonde adapted to be lowered
in a borehole traversing an earth formation, comprising the step of:
at least partially filling the housing with an insulating fluid having a
density greater than the density of a fluid present in the borehole, said
insulating fluid including a fluorinated organic compound.
2. The method according to claim 1 wherein said insulating fluid has a
density greater than the density of water.
3. The method according to claim 1 wherein said housing includes a mixture
of said insulating fluid and of a hydraulic oil the density of which is
less than the density of said insulating fluid.
4. The method according to claim 1 wherein said insulating fluid is
substantially not miscible with water.
5. The method according to claim 1 wherein said insulating fluid is
substantially not miscible with said borehole fluid.
6. The method according to claim 3 wherein said insulating fluid is
substantially not miscible with said hydraulic oil.
7. The method according to claim 1 wherein said insulating fluid is the
product sold under the name Fluorinert.RTM. (trademark of 3M).
8. A logging sonde adapted to be lowered in a borehole traversing an earth
formation and comprising:
a housing provided with at least one electrical connector at one of its
ends, the housing being at least partly filled with a mixture of an
insulating fluid and hydraulic oil the density of which is less than the
density of said insulating fluid, said insulating fluid having a density
greater than the density of water and the density of a fluid present in
the borehole.
9. The logging sonde according to claim 8 wherein said insulating fluid is
substantially not miscible with said hydraulic oil.
10. The logging sonde according to claim 8, wherein said insulating fluid
covers said electrical devices when said sonde is substantially in the
upright position.
11. The logging sonde according to claim 8 wherein said insulating fluid is
substantially not miscible with said borehole fluid.
12. The logging sonde according to claim 8 wherein said insulating fluid is
substantially not miscible with water.
13. The logging sonde according to claim 8 wherein said insulating fluid is
made of a fluorinated organic compound.
14. The logging sonde according to claim 13 wherein said insulating fluid
is the product sold under the name Fluorinert.RTM. (trademark of 3M).
15. A method for providing electrical insulation to electrical devices
disposed at one end of a housing of a logging sonde adapted to be lowered
in a borehole traversing an earth formation, comprising the step of:
at least partially filling the housing with a mixture of an insulating
fluid and of a hydraulic oil the density of which is less than the density
of said insulating fluid, said insulating fluid having a density greater
than the density of a fluid present in the borehole.
16. The method of claim 15, wherein said insulating fluid is substantially
not miscible with said hydraulic oil.
17. A logging sonde adapted to be lowered in a borehole traversing an earth
formation and comprising:
a housing provided with at least one electrical connector at one of its
end, the housing being at least partly filled with an insulating fluid
having a density greater than the density of water and the density of a
fluid present in the borehole, said insulating fluid including a
fluorinated organic compound.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to well logging techniques, wherein a sonde
is lowered in a well or borehole to perform measurements from which are
derived information about the composition and/or the physical structure of
the earth formation surrounding the borehole, or the borehole fluid, or
the annulus including casing and cement located between the borehole wall
and the formation.
2. The Related Art
A logging sonde usually comprises a hollow cylindrical body or housing made
out of metal, and in which are disposed the sensitive devices designed to
perform the measurements and transmit the data via the cable to the
surface. The housing is designed to contain and to protect such sensitive
devices from the hostile environment of the borehole, including high
temperature, high pressure and chemical/mechanical aggressions.
In order to counter balance the extremes forces which apply against the
external surface of the housing, or at least to reduce the differential
pressure between inside and outside of the housing, it is commonplace to
fill the housing with a fluid, usually oil. Such oil is usually referred
to as "hydraulic oil". Another purpose of hydraulic oil is, in electrical
type sondes, to electrically insulate the electrical sensitive devices,
such as coils, with respect to the housing wall and/or other conductive
elements or devices disposed in the housing and which might interfere
electrically with the coils. In sonic type sondes, a further purpose of
hydraulic oil is to enhance propagation of acoustic waves. A still further
purpose of hydraulic oil is to actuate hydraulic equipment such as pumps
or pistons in logging tools designed to extract a core from the formation,
as depicted in U.S. Pat. Nos. 4,714,119 and 3,596,511.
Furthermore, a sonde usually includes at each of its ends a pressure
bulkhead including an electrical connector designed to electrically link
the sensitive devices located inside of the housing to the electronic
cartridge disposed at the top of the sonde and which is linked to the
cable (at the upper end) or to another sonde (at the lower end).
These connectors must fulfill opposite requirements, since they must be
fluidproof, electrically and mechanically reliable as well as easy to
manipulate. These requirements are difficult to conciliate considering
that the working conditions encountered in a borehole are tough.
Nevertheless, sondes often face electrical problems at the level of the
electrical connector for the following reason. In spite of all precautions
taken avoid leaks in the housing, some borehole fluid penetration may
occur. These unwanted leaks mainly result from the repeated use of the
tool in a high pressure environment which imposes high flexing stresses on
seals. Practically, the hydraulic oil cannot be maintained 100% pure,
meaning there might be some water and/or borehole fluid mixed in the oil.
This is critical since hydraulic oil is partly miscible with water and
borehole fluid is most times, if not always, conductive, and may also
include some tiny metal fragments or debris resulting e.g. from wear.
Water, borehole fluid and debris entering through unwanted leaks in the
housing and contaminating the hydraulic oil, are heavier than the
hydraulic oil. They sooner or later find their way by gravity to the
bottom of the sonde, where the electrical connectors are located, and thus
affect the electrical insulation at the level of the connector. This may
put in jeopardy the operation of the sonde.
Accordingly, there is a need in the logging industry for improving
reliability of sondes and avoid the above referred problems.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to provide a reliable
electrical insulation at the level of the connectors disposed at the ends
of a logging sonde.
SUMMARY OF THE INVENTION
This and other objects of the invention are attained by a method for
providing electrical insulation to electrical devices disposed at at least
one end of the housing of a logging sonde designed to be lowered in a
borehole traversing earth formation, wherein the housing is at least
partly filled with an insulating fluid having a density greater than the
density of the fluid present in the borehole.
More particularly, the insulating fluid covers the electrical devices when
the sonde is substantially in th upright position.
The insulating fluid is preferably made of an organic compound sold under
the name Fluorinert.RTM. (trademark of 3M).
The invention will be readily understood upon reading of the following
description with reference to the drawing in which:
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 shows schematically an embodiment of an induction logging sonde in
accordance with the invention and the surface equipment connected to it;
FIG. 2 is a partly sectional longitudinal view of the sonde of FIG. 1;
FIG. 3 is a section according to line 3--3 of FIG. 2; and
FIG. 4 is schematic perspective view of an electrical connector disposed at
the end of the sonde.
DETAILED DESCRIPTION
The invention is not restricted or limited to particular oilfield services
or completion operations. Thus, the principles of the invention are
applicable for any well tool which has one or more components which need
electrical insulation and, for that purpose, are disposed in oil-filled
compartments, regardless of the type of wireline logging tool. By way of
illustrative example, the invention will be hereafter described in
connection with an induction logging tool, such as the one depicted in
U.S. Pat. No. 4,651,101 to T. D. Barber, R. N. Chandler and J. F. Hunka,
which is assigned to the assignee of this application and is hereby
incorporated by reference.
FIG. 1 shows an induction logging sonde 10 for investigating the geological
formations 11 traversed by a borehole 12. The borehole is filled with
drilling mud 13 (hereafter referred to as "borehole fluid"). The sonde 10
is suspended from a multiconductor cable 14 which passes on a sheave 15
and is wound on a winch 16 which is part of the surface equipment
associated with the downhole logging sonde. The surface equipment supplies
sonde 10 via cable 14 with electrical power and signals for controlling
its operation and receives from the downhole apparatus 10 measurement
signals. The surface equipment includes means 17 for processing and
recording these signals. A sensor 17a for detecting the motion of the
cable is provided. The signals from the sensor 17a are indicative of the
instantaneous depth of the sonde and are fed to the processing means for
depth matching the measurement signals.
The sonde 10 comprises at the top an electronic cartridge 18 connected to
the cable 14 through the cable head 19. The cartridge 18 includes a
telemetry cartridge 20 which converts the signals from the surface
equipment produced by the downhole apparatus to a format suitable for
transmission by the cable.
The sonde 10 also comprises an elongated support or housing 30 the upper
end of which is secured to the cartridge 18. The housing 30 mounts a coil
system which comprises a transmitting coil 31 and a receiving coil 32
coaxial to and spaced from each other in the longitudinal direction of
housing 30. The transmitting coil 31 is energized to produce a magnetic
field which induces in the formation eddy currents which flow coaxially of
the axis of the housing. The receiving coil 32 generates in response to
the field created by these currents an output signal representative of the
conductivity of the formation. The operating frequency of the transmitting
coil 31 is such that the displacement currents are negligible, conduction
currents being predominant, and typically lies between about 10 and about
400 kHz.
In the schematic drawing of FIG. 1, the sonde is shown to have only a
transmitting coil and a receiving coil but it will be clear that each coil
system can comprise more than two coils, for instance one or more
transmitters, several receiver coils, and bucking coils respectively
associated with the receiver coils to cancel out the effect of direct
coupling between the transmitter coil and the receiver coils. The sonde
could further comprise several coil systems distributed over its length.
The housing 30 has a generally tubular shape and is made of a metal,
preferably a non-magnetic metal having an excellent electrical
conductivity. The housing comprises cylindrical longitudinal portions 33
the outer walls 34 of which are in contact with the outside i.e. with the
borehole fluid, and cylindrical longitudinal portions 35 having an outside
diameter smaller than portions 33. The portions 35 thus define recesses
35a for receiving the coils 31 and 32 which are coaxial to and
electrically insulated from, the respective portions 35. The embodiment
shown in FIG. 1 includes such a recess for each coil, but it will be
understood that one portion 35 can as well mount an entire coil system,
i.e. one recess 35a can receive a plurality of axially spaced coils. The
intermediate portions 33 have preferably an inside diameter larger than
portions 35 and define inner spaces 36, and in the embodiment shown in
FIG. 1, the portions 33 and 35 are connected by transverse portions 37.
The walls of portions 33 have a sufficient thickness to withstand by
themselves the hydrostatic pressure of the borehole fluid. Respective
conductors 38 routed inside the support connect the coils 31 and 32 to the
electronic cartridge 18.
FIG. 2 shows in greater detail and in partly sectional view the induction
sonde of FIG. 1, comprising a transmitter coil unit 100 and a plurality of
arrays of solenoid coils, each coil array including a receiver coil and a
bucking coil designed and positioned so as to cancel out the effect of the
direct coupling of the transmitter coil to the respective receiver coil.
Receiver coils with different spacings from the transmitter are shown at
101, 102, and the bucking respectively associated with the receiver coils
are shown at 101', 102'. All the coils are mounted about a central support
105 having an outer cylindrical surface of circular cross-section. End
portions 106, 107 of enlarged diameter are secured to the support 105 at
both ends thereof. A housing 108, formed of a tubular sleeve of fiberglass
epoxy, is mounted about the coils to prevent contact with the borehole
fluid. The housing 108 is held in position between the end portions 106,
107, the housing having the same outer diameter as the end portions 106,
107. The free spaces in the annulus 110 defined between the central
support 105 and the housing 108 are filled with pressurized oil, called
"hydraulic oil", and to that effect, they are in communication with a
pressure compensation device, shown at 111 adjacent the lower end portion
107. The compensation device 111, a conventional element of well logging
sondes, acts to pressurize the oil present in the annulus 110 so that the
differential pressure on the housing 108 is small.
The cross section view of FIG. 3 shows a preferred embodiment of the
central support 105. the support 105 comprises two parts, an outer sleeve
115 preferably of a highly conductive metal such as copper or a copper
alloy, and an inner core 116 preferably of a metal of higher strength such
as stainless steel. The outer sleeve 115 is mounted over the inner core
116 with a loose fit to take into account the difference between copper
and steel with regard to thermal expansion. The inner core 116 has a
plurality of longitudinal grooves 117 formed in its outer periphery for
routing conductors. As shown in FIG. 3, the grooves 117 receive conductors
118 threaded inside a tubular shield 119. Although each groove can receive
a pair of conductors inside a shield, only one shield with conductors
inside has been shown in FIG. 3. The purpose of shield 119 is to minimize
interferences between the conductors located in adjacent grooves. The
shield can suitably be made of ferromagnetic material such as mumetal. In
addition to the grooves 117, the inner core has a central longitudinal
bore 120 which is used to route a power line and possibly conductors
connected to other logging apparatus suspended from the induction logging
sonde 10. The longitudinal grooves 117 and the central bore 120 are in
fluid communication with the annulus 110 through radial holes, not shown,
and therefore are filled with hydraulic oil at the same pressure as in the
annulus 110. A suitable method for manufacturing the inner core may be
extrusion through a die of appropriate design.
The electronic cartridge necessary for the operation of the transmitter is
schematically shown at 130 adjacent the lower end of the sonde, with a
pressure bulkhead 131 disposed between the compensation device 111 and the
cartridge 130. An electronic cartridge 132 connected to the receiver coils
is mounted adjacent the upper end of the sonde, with likewise a pressure
bulkhead 133 between the cartridge 132 and the coil section of the sonde.
The longitudinal grooves 117 are connected at their ends to inclined
passages 121 which open into the central bore 120.
The upper and lower pressure bulkheads 133, 131 are conventional pieces of
equipment in well logging sondes and have axially oriented passage
receiving pressure-resistant feedthroughs or connectors 150, 170, shown
with more details on FIG. 4, and to which conductors are connected on both
sides. Axially oriented passages 175, 176 are formed for the wires (not
shown) which link the connectors 150, 170 to the coils. The passages 176
communicate with the respective grooves 117 of support 105 through a
disc-shaped part 178 secured to the support and having a respective
plurality of radial slots for passing wires.
Only the general structure of the sonde and the elements critical to the
comprehension of the invention have been described hereabove for the sake
of clarity. More details on the structure and manufacturing of sonde 10
can be found in U.S. Pat. No. 4,651,101 already referred to.
FIG. 4 shows a schematic top perspective view of the upper connector 170
which is similar to connector 150. More details about this type of
connector can be found in U.S. Pat. No. 3,719,918. Connector 170 is
substantially cylindrical and comprises a central bore 180 in alignment
with bore 120 of central support 105. On both top and bottom sides of
connector 170 is provided a cylindrical scoop delimited in the
longitudinal direction by an annular transverse surface, only scoop 181
and surface 183 being visible on FIG. 4. Electrical pins, disposed e.g. by
pairs 184, 185, protrude from the transverse surface 183 and are angularly
regularly spaced. The electrical pins 184, 185 are linked through
electrical connections (known per se and not shown) to electrical wires
(such as wires 118 shown on FIG. 3) routed through spaces provided inside
the housing, these wires being e.g. connected to other logging apparatus
suspended from the induction logging sonde 10.
As already stated, free spaces inside housing 108 are filled with
pressurized hydraulic oil, for electrical insulation and mechanical
pressure balance purposes. Thus, the annulus 110 defined between central
support 105 and housing 108 (see FIG. 2), as well as longitudinal grooves
117 and the central bore 120 (see FIG. 3) are filled with pressurized
hydraulic oil. In particular, the electrical connections between the wires
(not shown) and the electrical pins 184, 185 are immersed in the hydraulic
oil. By way of example, the hydraulic oil might be oil sold under the name
UNIVIS J26 by EXXON.
According to the invention, inside housing 108 is provided a certain amount
of an insulating fluid, such as oil, showing good insulation properties
for the embodiment described, and having a density greater than the
density of the hydraulic oil and than the density of the borehole fluid.
Due to gravity, the insulating oil will be located, when the sonde is in
an upright position, at the bottom of housing 108, close to connector 150.
The amount of insulating oil may be such that, the sonde being
substantially vertical, the insulating oil covers the electrical
connections located at the bottom of the housing close to connector 150.
Typically, by way of example, the amount of insulating oil could be in the
range of 50-300 cubic centimeters (cc), and preferably around 100 cc. In a
similar way, any amount of borehole fluid or debris, that typically
penetrates the sonde and thus contaminates the hydraulic oil, will find
its way down inside the housing, since it is, in most of the cases,
heavier than the hydraulic oil. However, the insulating oil, being heavier
than these contaminating fluids or debris, will prevent the latter to
reach the electrical connections, since the hydraulic oil will be placed
above the layer or insulating oil and thus the contaminating fluid or
debris which may be present in the hydraulic oil will not be in contact
with the electrical connections. By way of example, the density of the
insulating oil may be greater than 1.5. The amount of insulating oil will
determine the position in the tool of the interface between the insulating
oil and the hydraulic oil, said interface being associated with water or
debris. Thus, this will determine the height of this contaminating
products in the upright position of the tool. The amount of insulating oil
could be tailored so as to bring these contaminating products at a given
level in the tool where the danger of electrical damages are reduced if
not absent.
The insulating oil has to fulfill the specifications required for the
associated hydraulic oil. For example, in coring tools, the insulating oil
has to be compatible with the hydraulic equipment such as pumps and
pistons.
A further characteristic of the insulating oil is its non miscibility with
water, hydraulic oil and borehole fluid.
The insulating oil is preferably made of fluorinated organic compound,
derived from organic compounds where all carbon-bound hydrogen atoms are
replaced by fluorine atoms. By way of example, the insulating oil may be
the oil sold under the name Fluorinert.RTM. (trademark of 3M).
As an alternative embodiment, the housing instead of being completely
filled with a mixture of hydraulic oil and insulating oil, may be filled
in with insulating oil only, by an amount enough to cover electrical
connections in vertical position of the sonde. Since insulating oil is not
miscible with water or borehole fluids, such oil is reusable, unlike the
hydraulic oil. In other words, during any regular maintenance check-up, it
can be submitted to simple cleaning process such as filtering and be
poured back into the tool.
According to another implementation, a logging sonde of relatively small
volume (a few hundreds of cc) is filled with insulating oil. Whenever
water or borehole fluid penetrates the sonde, such fluid will position
itself above the insulating oil, i.e. at the top. Accordingly, when
carrying out a check or maintenance operation, the operator opens up the
sonde (in vertical position), pours some insulating oil inside the sonde
which actually expels the water. An appropriate example of such sonde is a
sonde designed to carry out auxiliary measurements; such sonde is usually
disposed at the top of the tool string.
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